An increasing number of fuel injectors are being machined to include a direct control needle valve. In operation, a direct control needle valve is moved between an open position and a closed position by fluid displacement. For instance, the direct control needle valve to move from its closed position toward its open position, a small amount of fluid must be displaced by the needle valve. Similarly, for the needle valve to move from its open position to its closed position, a small amount of fluid must be displaced toward the needle valve. Use of direct control needle valves is desirable because they can allow for greater control over fuel injection events. Engineers have learned that the ability to better control fuel injection events can include a number of advantages, such as improved injector performance and a reduction in undesirable emissions.
In this regard, it has been learned that a fast needle valve closing is desirable to produce an abrupt end to the injection event. Conversely, it has been determined that a slow needle valve opening can increase needle valve control at the beginning of an injection event. Several attempts have been made to increase control over fuel injection events. One such attempt is disclosed in U.S. Pat. No. 6,024,296, which issued to Wear et al. on Feb. 15, 2000. Wear et al. discloses a fuel injector having a needle control passage that includes a dual flow rate orifice. While Wear et al. shows promise, there is still room for improvement.
The present invention is directed to overcoming one or more of the problems as set forth above.